Drosophila has served as a model for understanding the molecular genetics of innate immunity, but the cellular part of the innate immune system remains poorly characterized at the molecular level. Furthermore, there are very few model systems available for studying the genetic basis of natural host-pathogen interactions, particularly between eukaryotic hosts and pathogens, and developing one utilizing a host with the array of genetic tools available in Drosophila would be especially valuable. In previous work, we identified a number of candidate Drosophila genes thought to play a role in the fly cellular immune response against endoparasitoid wasps, including genes involved in pattern recognition, hemocyte (blood cell) signaling, and cytoskeletal modifications necessary for hemocyte migration and encapsulation of wasp eggs (Schlenke et al. 2007). Here, we propose a series of experiments aimed at understanding the molecular and evolutionary interactions between the Drosophila cellular immune response and the immune suppressive venom components of its natural wasp macroparasites. We will functionally characterize candidate Drosophila anti-wasp immunity genes, and genetically map Drosophila loci responsible for genetic variation in wasp killing success in natural populations. We will also tackle the wasp side of the equation by identifying venom proteins from the venom glands of two closely related wasps with divergent infection strategies, using a combination of cDNA library and protein sequencing. The cDNA sequences will be used to generate markers to genetically map wasp loci responsible for genetic variation in wasp infection success in natural populations. Finally, we will study the molecular evolutionary history of the wasp-fly interaction by collecting DNA polymorphism and divergence data from natural populations for Drosophila immune genes and wasp venom genes, and by inferring the past selection pressures on these genes using standard population genetics and molecular evolution techniques. PUBLIC HEALTH RELEVANCE: The purpose of this project is to understand the molecular and evolutionary interactions between the Drosophila cellular immune response and the venom components of its wasp macroparasites. This work will uncover basic elements of the Drosophila innate immune system, mechanisms by which generalist and specialist parasites suppress the immune response, and the fly immune genes and wasp venom genes that engage in antagonistic interactions over evolutionary time.